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At high latitudes, the electric field and precipitating particles originated in the magnetosphere significantly affect motions of ions.  Motions of ions during geomagnetically active intervals can disturb those of neutrals in the auroral thermosphere through collisions between ions and neutrals.  For example, wavelike structures in the motions of neutrals at oscillation periods from a few tens minutes to a few hours are generated by enhancements of plasma flow, or the electric field [Hunsucker, 1982 and references therein].  For more than four decades, wavelike structures such as gravity waves in the thermosphere have been the subject of many theoretical and experimental studies on thermospheric and ionospheric motions during auroral activity.  There are, however, many unresolved aspects of the wavelike structures in the auroral ionosphere and thermosphere. 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Our observation is the first simultaneous experiment using optical and radio techniques for targeting on short-time-scale oscillations of ions and neutrals in the auroral F-region.  In general, it is difficult to obtain optical data of sufficient quality successively, but the field-aligned velocities obtained during this campaign have good quality with time-resolution of about 1.5min and can be used to investigate dynamical coupling between oscillations of ions and neutrals in short time-scale.  The summary of the EISCAT-FPI comparison is that the amplitude and the phase of U_//FPI have been correctly estimated using EISCAT radar data as long as the height range covered by EISCAT radar data in use has overlapped the emission layer.  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  1. B100 理学部/理学研究科
  2. B100d 学位論文
  3. 博士論文(理博・論理博)

Dynamical coupling of plasma motions and neutral winds in the presence of short time-scale(10-90 min)wavelike structures in the auroral ionosphere

http://hdl.handle.net/2237/11221
http://hdl.handle.net/2237/11221
04fba081-2050-43a6-9c5c-513e4083ce37
名前 / ファイル ライセンス アクション
ko4940.pdf ko4940.pdf (8.6 MB)
Item type 学位論文 / Thesis or Dissertation(1)
公開日 2009-03-02
タイトル
タイトル Dynamical coupling of plasma motions and neutral winds in the presence of short time-scale(10-90 min)wavelike structures in the auroral ionosphere
言語 en
その他のタイトル
その他のタイトル オーロラ帯電離圏において短周期(10-90分)の波状構造を持つプラズマおよび中性大気運動の力学的結合
言語 ja
著者 大山, 伸一郎

× 大山, 伸一郎

WEKO 26943

ja 大山, 伸一郎

Search repository
Oyama, Shin-ichiro

× Oyama, Shin-ichiro

WEKO 26944

en Oyama, Shin-ichiro

Search repository
アクセス権
アクセス権 open access
アクセス権URI http://purl.org/coar/access_right/c_abf2
抄録
内容記述 Ions in the ionosphere are drifted through the process of the cross product of the electric and magnetic fields, momentum transfer from neutrals to ions through collisions, and diffusion caused by the pressure gradient mainly along geomagnetic field lines. At high latitudes, the electric field and precipitating particles originated in the magnetosphere significantly affect motions of ions. Motions of ions during geomagnetically active intervals can disturb those of neutrals in the auroral thermosphere through collisions between ions and neutrals. For example, wavelike structures in the motions of neutrals at oscillation periods from a few tens minutes to a few hours are generated by enhancements of plasma flow, or the electric field [Hunsucker, 1982 and references therein]. For more than four decades, wavelike structures such as gravity waves in the thermosphere have been the subject of many theoretical and experimental studies on thermospheric and ionospheric motions during auroral activity. There are, however, many unresolved aspects of the wavelike structures in the auroral ionosphere and thermosphere. Two of them are, (1) dynamical coupling of plasma motions and neutral winds in the presence of wavelike structures in short time-scale (10-90 min) in the auroral ionosphere, and (2) relationships between wavelike structures and ionospheric disturbances in association with auroral acts. We conduct three analyses on these topics using data observed mainly with the European Incoherent Scatter (EISCAT) radar, a scanning Fabry-Perot interferometer (FPI), and an all-sky auroral camera:・Dynamical coupling between oscillations of ions and neutrals in short timescale from simultaneous observations between the EISCAT radar and the scanning FPI (λ= 630.0nm),・Statistical analysis of the ion velocity, along the geomagnetic field line, observed with the KST (Kiruna-sodankylä -Troms ø) EISCAT radar and ESR (EISCAT Svalbard Radar), ・Relationship between wavelike structures and ionospheric disturbances in association with auroral arcs using data from simultaneous observations between the EISCAT radar and the all-sky auroral camera.Field-aligned velocities of ions and neutrals in almost the same volume in the F-region have been obtained at the same time with the EISCAT radar and the scanning FPI during the night of 8 February 1997 at Troms ø, Norway. Our observation is the first simultaneous experiment using optical and radio techniques for targeting on short-time-scale oscillations of ions and neutrals in the auroral F-region. In general, it is difficult to obtain optical data of sufficient quality successively, but the field-aligned velocities obtained during this campaign have good quality with time-resolution of about 1.5min and can be used to investigate dynamical coupling between oscillations of ions and neutrals in short time-scale. The summary of the EISCAT-FPI comparison is that the amplitude and the phase of U_//FPI have been correctly estimated using EISCAT radar data as long as the height range covered by EISCAT radar data in use has overlapped the emission layer. It is concluded that the plasma oscillations observed with the EISCAT radar at different heights in the F-region are thought to be due to the motion of neutrals.The main conclusion of the statistical study on the field-aligned ion motions using KST radar and ESR data is that diurnal variations in the field-aligned ion motion are likely driven by the large-scale pressure gradient of the temperature of neutrals. Sporadic/burst upward ion motions along geomagnetic field lines are observed during enhancements of the southward electric field. Plasma diffusion velocities during large upward ion-motion events are significantly smaller than the magnitude of the observed upward velocity, which suggests that neutral winds in the F-region should strongly affect the generation of the large upward ion velocities. However, we do not yet understood driving mechanisms of those upward ion motions and the relation between motions of neutrals and ionospheric heating caused by enhancement of the electric field. The simultaneous observations using the EISCAT radar and the all-sky camera were conducted in northern Scandinavia on 1 March 1995 and revealed wavelike structures of the neutral-wind velocity in the auroral F-region and ionospheric disturbances in association with auroral arcs. Although we cannot find conclusive evidence that the observed oscillations are gravity waves (GWs), the wave parameters, such as frequency, phase, and wavelength, of observed oscillations are typical one for medium-scale GWs according to Hunsucker [1982]. From the wave parameters, we estimate when and where the observed oscillations have been generated using the dispersion relation for GWs. Around the estimated position and time, the auroral arc has extended in an almost zonal direction according to all-sky auroral images obtained at Kilpisjävi. This implies that geomagnetic activity at high latitudes is important to generate GWs, as indicated by previous theoretical studies.
言語 en
内容記述タイプ Abstract
内容記述
内容記述 名古屋大学博士学位論文 学位の種類:博士(理学) (課程) 学位授与年月日:平成13年3月26日
言語 ja
内容記述タイプ Other
言語
言語 eng
資源タイプ
資源 http://purl.org/coar/resource_type/c_db06
タイプ doctoral thesis
書誌情報
発行日 2001-03-26
学位名
言語 ja
学位名 博士(理学)
学位授与機関
学位授与機関識別子Scheme kakenhi
学位授与機関識別子 13901
言語 ja
学位授与機関名 名古屋大学
言語 en
学位授与機関名 Nagoya University
学位授与年度
学位授与年度 2000
学位授与年月日
学位授与年月日 2001-03-26
学位授与番号
学位授与番号 甲第4940号
フォーマット
application/pdf
著者版フラグ
値 publisher
URI
識別子 http://hdl.handle.net/2237/11221
識別子タイプ HDL
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